feat(setup): add a setup token for first-run setup (#3437)

2026-10-17 21:15:32 +09:00 · 2026-10-13 00:17:24 +02:00
1 parent 8e39380ee6
commit 78272521bb
@@ -259,3 +259,42 @@ describe('buildAPIConfigFromMaster trusted callers', () => {
 		);
 	});
 });
+
+async function setupTokenFromEnv(env: Record<string, string>): Promise<string | null> {
+	for (const [key, value] of Object.entries(env)) {
+		vi.stubEnv(key, value);
+	}
+	resetConfig();
+	return buildAPIConfigFromMaster(await loadConfig()).instance.setup.token;
+}
+
+describe('buildAPIConfigFromMaster setup token', () => {
+	const setupToken = 's'.repeat(32);
+
+	test('reads the token from FLUXER_SETUP_TOKEN', async () => {
+		expect(await setupTokenFromEnv({FLUXER_SETUP_TOKEN: ` ${setupToken}\n`})).toBe(setupToken);
+	});
+
+	test.each(['', '  '])('leaves the token unset for %j', async (blank) => {
+		expect(await setupTokenFromEnv({FLUXER_SETUP_TOKEN: blank})).toBeNull();
+	});
+
+	test('leaves the token unset when the variable is missing', async () => {
+		expect(await setupTokenFromEnv({})).toBeNull();
+	});
+
+	test('accepts a token of 256 characters', async () => {
+		expect(await setupTokenFromEnv({FLUXER_SETUP_TOKEN: 's'.repeat(256)})).toBe('s'.repeat(256));
+	});
+
+	test.each([
+		['shorter than 32 characters', 's'.repeat(31)],
+		['longer than 256 characters', 's'.repeat(257)],
+		['holding a form feed', `${'s'.repeat(16)}\f${'s'.repeat(16)}`],
+		['holding a text direction override', `${'s'.repeat(16)}\u202E${'s'.repeat(16)}`],
+	])('fails at boot on a token %s', async (_case, token) => {
+		await expect(setupTokenFromEnv({FLUXER_SETUP_TOKEN: token})).rejects.toThrow(
+			'FLUXER_SETUP_TOKEN must be 32 to 256 printable characters',
+		);
+	});
+});
@@ -8,6 +8,7 @@ import type {WorkerTaskName} from '@app/api/worker/WorkerLaneConfig';
 import type {MasterConfig} from '@fluxer/config/src/MasterConfig';
 import {smtpTlsModeFromSecure} from '@fluxer/constants/src/SmtpConstants';
 import {parseIpAddress} from '@fluxer/ip_utils/src/IpAddress';
+import {normalizeString} from '@fluxer/schema/src/primitives/SchemaPrimitives';
 import {parseGeoipSourceConfig, resolveGeoipRuntimeSourceConfig} from '@pkgs/geoip/src/GeoipStartup';

 function extractHostname(url: string): string {
@@ -123,6 +124,24 @@ function buildTrustedCallers(master: MasterConfig): Array<TrustedCallerConfig> {
 	return trustedCallers;
 }

+const SETUP_TOKEN_MIN_LENGTH = 32;
+const SETUP_TOKEN_MAX_LENGTH = 256;
+
+function resolveSetupToken(master: MasterConfig): string | null {
+	const token = master.instance.setup.token?.trim();
+	if (!token) return null;
+	if (
+		token.length < SETUP_TOKEN_MIN_LENGTH ||
+		token.length > SETUP_TOKEN_MAX_LENGTH ||
+		normalizeString(token) !== token
+	) {
+		throw new Error(
+			`FLUXER_SETUP_TOKEN must be ${SETUP_TOKEN_MIN_LENGTH} to ${SETUP_TOKEN_MAX_LENGTH} printable characters`,
+		);
+	}
+	return token;
+}
+
 export function buildAPIConfigFromMaster(master: MasterConfig): APIConfig {
 	if (!master.internal) {
 		throw new Error('internal configuration is required for the API');
@@ -402,6 +421,7 @@ export function buildAPIConfigFromMaster(master: MasterConfig): APIConfig {
 			},
 			setup: {
 				configured: master.instance.setup.configured,
+				token: resolveSetupToken(master),
 			},
 			accountIdentity: master.instance.account_identity,
 			tagStyle: master.instance.tag_style,
@@ -11,6 +11,7 @@ import {
 	REGISTRATION_PENDING_APPROVAL_TRAIT,
 	REGISTRATION_REJECTED_TRAIT,
 } from '@app/api/instance/InstanceConfigRepository';
+import {clearUsedSetupToken} from '@app/api/instance/SetupToken';
 import {deriveSsoRedirectUri, normalizeAndValidateSsoConfig} from '@app/api/instance/SsoConfigValidation';
 import {requireAdminACL} from '@app/api/middleware/AdminMiddleware';
 import {RateLimitMiddleware} from '@app/api/middleware/RateLimitMiddleware';
@@ -44,7 +45,6 @@ import {ExperimentDeliveryConfigSchema} from '@fluxer/schema/src/domains/experim
 import type {InstanceBranding} from '@fluxer/schema/src/domains/instance/InstanceSchemas';
 import {SmtpEmailProvider} from '@pkgs/email/src/SmtpEmailProvider';
 import type {Context} from 'hono';
-import {createMiddleware} from 'hono/factory';

 const INSTANCE_BRANDING_ENTITY_ID = 0n;
 const ATTACHMENT_EXPIRY_RULE_FIELDS = [
@@ -187,49 +187,6 @@ function buildAdminIssuedRegistrationUrl(code: string): string {
 	return `${baseUrl}/register?registration_url=${encodeURIComponent(code)}`;
 }

-function requireSetupSessionOrAdminACL(requiredACL: string) {
-	const requireAcl = requireAdminACL(requiredACL);
-	return createMiddleware<HonoEnv>(async (ctx, next) => {
-		const user = ctx.get('user');
-		const tokenType = ctx.get('authTokenType');
-		if (user && tokenType === 'session') {
-			const appPublic = await getInstanceConfigRepository().getAppPublicConfig();
-			if (!appPublic.setup.configured) {
-				ctx.set('adminUserId', user.id);
-				ctx.set('adminUserAcls', user.acls);
-				await next();
-				return;
-			}
-		}
-		return requireAcl(ctx, next);
-	});
-}
-
-function hasAdminAuthenticationACL(acls: ReadonlySet<string>): boolean {
-	return acls.has(AdminACLs.AUTHENTICATE) || acls.has(AdminACLs.WILDCARD);
-}
-
-function completesInitialSetup(data: InstanceConfigUpdateRequest, setupConfigured: boolean): boolean {
-	return (
-		!setupConfigured &&
-		data.app_public?.setup != null &&
-		readOptionalField(data.app_public.setup, 'configured') === true
-	);
-}
-
-async function grantSetupCompleterAdminACL(ctx: Context<HonoEnv>): Promise<boolean> {
-	const user = ctx.get('user');
-	if (!user || ctx.get('authTokenType') !== 'session' || hasAdminAuthenticationACL(user.acls)) {
-		return false;
-	}
-	const nextACLs = new Set(user.acls);
-	nextACLs.add(AdminACLs.WILDCARD);
-	const updatedUser = await ctx.get('userRepository').patchUpsert(user.id, {acls: nextACLs}, user.toRow());
-	ctx.set('user', updatedUser);
-	ctx.set('adminUserAcls', updatedUser.acls);
-	return true;
-}
-
 function relayConsentStamp(
 	current: PushRelayConfig,
 	patch: PushRelayConfigUpdateRequest,
@@ -346,7 +303,7 @@ export function InstanceConfigAdminController(app: HonoApp) {
 	app.get(
 		'/admin/instance/config',
 		RateLimitMiddleware(RateLimitConfigs.ADMIN_LOOKUP),
-		requireSetupSessionOrAdminACL(AdminACLs.INSTANCE_CONFIG_VIEW),
+		requireAdminACL(AdminACLs.INSTANCE_CONFIG_VIEW),
 		OpenAPI({
 			operationId: 'get_admin_instance_config',
 			summary: 'Get instance configuration',
@@ -374,7 +331,7 @@ export function InstanceConfigAdminController(app: HonoApp) {
 	app.patch(
 		'/admin/instance/config',
 		RateLimitMiddleware(RateLimitConfigs.ADMIN_USER_MODIFY),
-		requireSetupSessionOrAdminACL(AdminACLs.INSTANCE_CONFIG_UPDATE),
+		requireAdminACL(AdminACLs.INSTANCE_CONFIG_UPDATE),
 		Validator('json', InstanceConfigUpdateRequest),
 		OpenAPI({
 			operationId: 'update_admin_instance_config',
@@ -390,11 +347,6 @@ export function InstanceConfigAdminController(app: HonoApp) {
 			const data = ctx.req.valid('json');
 			assertSelfHostedBillingSections(data);
 			await assertBillingCompatibleWithPremiumMode(data);
-			const appPublicBeforeUpdate = completesInitialSetup(data, false)
-				? await instanceConfigRepository.getAppPublicConfig()
-				: null;
-			const shouldGrantSetupCompleterAdmin =
-				appPublicBeforeUpdate !== null && completesInitialSetup(data, appPublicBeforeUpdate.setup.configured);
 			if (data.gateway_rollout) {
 				const patch = data.gateway_rollout;
 				const landed = await instanceConfigRepository.updateGatewayRolloutConfig((current) =>
@@ -628,16 +580,14 @@ export function InstanceConfigAdminController(app: HonoApp) {
 				);
 			}
 			if (data.app_public?.setup) {
+				const configured = readOptionalField(data.app_public.setup, 'configured');
 				await instanceConfigRepository.setAppPublicConfig({
-					setup: omitUndefinedFields({
-						configured: readOptionalField(data.app_public.setup, 'configured'),
-					}),
+					setup: omitUndefinedFields({configured}),
 				});
-			}
-			let grantedSetupCompleterAdmin = false;
-			if (shouldGrantSetupCompleterAdmin) {
-				grantedSetupCompleterAdmin = await grantSetupCompleterAdminACL(ctx);
-				await instanceConfigRepository.markAdminBootstrapped();
+				if (configured === true) {
+					await instanceConfigRepository.claimAdminBootstrap();
+					await clearUsedSetupToken(instanceConfigRepository);
+				}
 			}
 			await recordAdminWrite(ctx, {
 				targetType: 'instance_config',
@@ -645,7 +595,6 @@ export function InstanceConfigAdminController(app: HonoApp) {
 				action: 'update_instance_config',
 				metadata: {
 					sections: listSuppliedSections(data),
-					granted_acls: grantedSetupCompleterAdmin ? AdminACLs.WILDCARD : undefined,
 				},
 			});
 			return ctx.json(await buildInstanceConfigResponse());
@@ -654,7 +603,7 @@ export function InstanceConfigAdminController(app: HonoApp) {
 	app.post(
 		'/admin/instance/config/branding-assets',
 		RateLimitMiddleware(RateLimitConfigs.ADMIN_USER_MODIFY),
-		requireSetupSessionOrAdminACL(AdminACLs.INSTANCE_CONFIG_UPDATE),
+		requireAdminACL(AdminACLs.INSTANCE_CONFIG_UPDATE),
 		Validator('json', BrandingAssetUploadRequest),
 		OpenAPI({
 			operationId: 'create_admin_instance_branding_asset',
@@ -690,7 +639,7 @@ export function InstanceConfigAdminController(app: HonoApp) {
 	app.post(
 		'/admin/instance/config/smtp-tests',
 		RateLimitMiddleware(RateLimitConfigs.ADMIN_USER_MODIFY),
-		requireSetupSessionOrAdminACL(AdminACLs.INSTANCE_CONFIG_UPDATE),
+		requireAdminACL(AdminACLs.INSTANCE_CONFIG_UPDATE),
 		Validator('json', InstanceEmailSmtpTestRequest),
 		OpenAPI({
 			operationId: 'create_admin_instance_smtp_test',
@@ -27,7 +27,6 @@ export const InstanceConfigAdminAuditCases: ReadonlyArray<AdminAuditCoverageCase
 	{
 		method: 'GET',
 		route: '/admin/instance/config',
-		name: 'admin acl',
 		async prepare({harness, admin}) {
 			await createRegistrationUrl(harness, admin);
 			return {
@@ -41,23 +40,6 @@ export const InstanceConfigAdminAuditCases: ReadonlyArray<AdminAuditCoverageCase
 			};
 		},
 	},
-	{
-		method: 'GET',
-		route: '/admin/instance/config',
-		name: 'setup session',
-		async prepare() {
-			await getInstanceConfigRepository().setAppPublicConfig({setup: {configured: false}});
-			return {
-				request: {path: '/admin/instance/config'},
-				expected: {
-					action: 'get_instance_config',
-					targetType: 'instance_config',
-					targetId: '0',
-					metadata: {registration_url_count: '0', pending_registration_count: '0'},
-				},
-			};
-		},
-	},
 	{
 		method: 'PATCH',
 		route: '/admin/instance/config',
@@ -12,8 +12,10 @@ import {createPasswordResetToken} from '@app/api/BrandedTypes';
 import {Config} from '@app/api/Config';
 import type {UserRow} from '@app/api/database/types/UserTypes';
 import {Logger} from '@app/api/Logger';
+import {getKVClient} from '@app/api/middleware/ServiceRegistry';
 import {getInstanceConfigRepository} from '@app/api/middleware/ServiceSingletons';
 import type {User} from '@app/api/models/User';
+import {PASSWORD_RESET_TOKEN_TTL_SECONDS} from '@app/api/user/repositories/auth/TokenRepository';
 import {EXTERNAL_RESPONSE_LIMITS} from '@app/api/utils/ExternalResponseLimits';
 import * as FetchUtils from '@app/api/utils/FetchUtils';
 import {hashPassword} from '@app/api/utils/PasswordUtils';
@@ -31,6 +33,7 @@ import {ms} from 'itty-time';

 const PWNED_PASSWORDS_TIMEOUT_MS = ms('5 seconds');
 const PWNED_PASSWORD_CACHE_MAX_PREFIXES = 128;
+const PASSWORD_RESET_CLAIM_KEY_PREFIX = 'auth:password-reset:claimed:';

 interface CacheEntry {
 	pwnedSuffixes: ReadonlySet<string>;
@@ -94,12 +97,14 @@ interface ApplyPasswordResetParams {
 	password: string;
 	request: Request;
 	afterPasswordSet?: () => Promise<void>;
+	onPasswordWritten?: () => void;
 }

 interface CommitPasswordResetParams {
 	user: User;
 	passwordHash: string;
 	webauthnIsSecondFactor: boolean;
+	onPasswordWritten?: () => void;
 }

 type ResetPasswordResult =
@@ -242,6 +247,22 @@ export async function validateResetToken(ctx: ApiContext, token: string): Promis
 	return true;
 }

+function passwordResetClaimKey(token: string): string {
+	return `${PASSWORD_RESET_CLAIM_KEY_PREFIX}${crypto.createHash('sha256').update(token).digest('hex')}`;
+}
+
+function claimPasswordResetToken(token: string): Promise<boolean> {
+	return getKVClient().setnx(passwordResetClaimKey(token), '1', PASSWORD_RESET_TOKEN_TTL_SECONDS);
+}
+
+async function releasePasswordResetTokenClaim(token: string): Promise<void> {
+	try {
+		await getKVClient().del(passwordResetClaimKey(token));
+	} catch (error) {
+		Logger.error({error}, 'Could not release the claim of a password reset token whose reset failed');
+	}
+}
+
 export async function resetPassword(
 	ctx: ApiContext,
 	{data, request}: ResetPasswordParams,
@@ -263,28 +284,42 @@ export async function resetPassword(
 	if (await isPasswordPwned(ctx, data.password)) {
 		throw InputValidationError.fromCode('password', ValidationErrorCodes.PASSWORD_IS_TOO_COMMON);
 	}
-	if (tokenData.email !== null) {
+	if (!(await claimPasswordResetToken(data.token))) {
+		throw InputValidationError.fromCode('token', ValidationErrorCodes.INVALID_OR_EXPIRED_RESET_TOKEN);
+	}
+	let passwordWritten = false;
+	const onPasswordWritten = () => {
+		passwordWritten = true;
+	};
+	try {
+		if (tokenData.email !== null) {
+			return await applyPasswordReset(ctx, {
+				user,
+				password: data.password,
+				request,
+				afterPasswordSet: () => users.deleteAllPasswordResetTokens(user.id),
+				onPasswordWritten,
+			});
+		}
 		return await applyPasswordReset(ctx, {
-			user,
+			user: currentUser,
 			password: data.password,
 			request,
-			afterPasswordSet: () => users.deleteAllPasswordResetTokens(user.id),
+			afterPasswordSet: async () => {
+				await users.deleteAllPasswordResetTokens(currentUser.id);
+				await new RecoveryKitRepository().delete(currentUser.id);
+			},
+			onPasswordWritten,
 		});
+	} catch (error) {
+		if (!passwordWritten) await releasePasswordResetTokenClaim(data.token);
+		throw error;
 	}
-	return await applyPasswordReset(ctx, {
-		user: currentUser,
-		password: data.password,
-		request,
-		afterPasswordSet: async () => {
-			await users.deleteAllPasswordResetTokens(currentUser.id);
-			await new RecoveryKitRepository().delete(currentUser.id);
-		},
-	});
 }

 export async function commitPasswordReset(
 	ctx: ApiContext,
-	{user, passwordHash, webauthnIsSecondFactor}: CommitPasswordResetParams,
+	{user, passwordHash, webauthnIsSecondFactor, onPasswordWritten}: CommitPasswordResetParams,
 ): Promise<User> {
 	const {users} = ctx.services;
 	const updates: Partial<UserRow> = {
@@ -297,6 +332,7 @@ export async function commitPasswordReset(
 		updates.authenticator_types = authenticatorTypes;
 	}
 	const updatedUser = await users.patchUpsert(user.id, updates, user.toRow());
+	onPasswordWritten?.();
 	if (updates.authenticator_types) {
 		await ctx.services.botMfaMirror.syncAuthenticatorTypesForOwner(updatedUser);
 	}
@@ -306,12 +342,12 @@ export async function commitPasswordReset(

 export async function applyPasswordReset(
 	ctx: ApiContext,
-	{user, password, request, afterPasswordSet}: ApplyPasswordResetParams,
+	{user, password, request, afterPasswordSet, onPasswordWritten}: ApplyPasswordResetParams,
 ): Promise<ResetPasswordResult> {
 	const webauthnIsSecondFactor = await resolveWebAuthnSecondFactor(ctx, user);
 	const hasMfa = user.authenticatorTypes.has(UserAuthenticatorTypes.TOTP) || webauthnIsSecondFactor;
 	const passwordHash = await hashPassword(password);
-	const updatedUser = await commitPasswordReset(ctx, {user, passwordHash, webauthnIsSecondFactor});
+	const updatedUser = await commitPasswordReset(ctx, {user, passwordHash, webauthnIsSecondFactor, onPasswordWritten});
 	await afterPasswordSet?.();
 	if (hasMfa) {
 		return await createMfaTicketResponse(ctx, updatedUser, webauthnIsSecondFactor);
@@ -25,6 +25,7 @@ import {
 	REGISTRATION_PENDING_APPROVAL_TRAIT,
 	type RegistrationUrlClaim,
 } from '@app/api/instance/InstanceConfigRepository';
+import {assertSetupToken, clearUsedSetupToken, isSetupTokenEnforced} from '@app/api/instance/SetupToken';
 import type {SingleCommunityService} from '@app/api/instance/SingleCommunityService';
 import type {InviteService} from '@app/api/invite/InviteService';
 import {Logger} from '@app/api/Logger';
@@ -85,6 +86,11 @@ interface RegisterParams {
 	requestCache: RequestCache;
 }

+interface RegisterAccountParams extends RegisterParams {
+	clientIp: string;
+	setupTokenVerified: boolean;
+}
+
 export interface RegistrationDependencies {
 	inviteService: InviteService;
 	instanceConfigRepository: InstanceConfigRepository;
@@ -114,16 +120,26 @@ export async function register(
 	deps: RegistrationDependencies,
 	params: RegisterParams,
 ): Promise<RegisterResult> {
-	if (!ctx.services.config.instance.selfHosted || (await deps.instanceConfigRepository.isAccountIdentityLocked())) {
-		return await registerAccount(ctx, deps, params);
+	const {config, rateLimit, cache} = ctx.services;
+	const clientIp = requireConfiguredClientIp(params.request, config.proxy);
+	const setupTokenVerified = await assertSetupToken({
+		rateLimit,
+		config,
+		repository: deps.instanceConfigRepository,
+		presented: params.data.setup_token,
+		clientIp,
+	});
+	const account = {...params, clientIp, setupTokenVerified};
+	if (!config.instance.selfHosted || (await deps.instanceConfigRepository.isAccountIdentityLocked())) {
+		return await registerAccount(ctx, deps, account);
 	}
-	return await withAccountIdentitySetupLock(ctx.services.cache, () => registerAccount(ctx, deps, params));
+	return await withAccountIdentitySetupLock(cache, () => registerAccount(ctx, deps, account));
 }

 async function registerAccount(
 	ctx: ApiContext,
 	deps: RegistrationDependencies,
-	{data, request, requestCache}: RegisterParams,
+	{data, request, requestCache, clientIp, setupTokenVerified}: RegisterAccountParams,
 ): Promise<RegisterResult> {
 	const {users, snowflake, emailDnsValidation, config} = ctx.services;
 	const {inviteService, instanceConfigRepository, singleCommunityService, discriminatorService, kvActivityTracker} =
@@ -144,8 +160,9 @@ async function registerAccount(
 		throw InputValidationError.fromCode('consent', ValidationErrorCodes.MUST_AGREE_TO_TOS_AND_PRIVACY_POLICY);
 	}
 	const now = new Date();
-	const registrationAccess = await resolveRegistrationAccess(instanceConfigRepository, data.registration_url_code);
-	const clientIp = requireConfiguredClientIp(request, config.proxy);
+	const registrationAccess = setupTokenVerified
+		? {pendingApproval: false, registrationUrl: null}
+		: await resolveRegistrationAccess(instanceConfigRepository, data.registration_url_code);
 	const geoipResult = await lookupGeoip(clientIp);
 	const countryCode = geoipResult.countryCode;
 	const collectDateOfBirth = appPublicConfig.registration.collect_date_of_birth;
@@ -168,7 +185,7 @@ async function registerAccount(
 	}
 	const rawEmail = usernameMode ? null : (data.email ?? null);
 	const emailKey = rawEmail ? rawEmail.toLowerCase() : null;
-	const enforceRateLimits = !config.dev.relaxRegistrationRateLimits;
+	const enforceRateLimits = !config.dev.relaxRegistrationRateLimits && !setupTokenVerified;
 	await enforceRegistrationRateLimits(ctx, {enforceRateLimits, clientIp, emailKey});
 	if (rawEmail) {
 		if (isBlockedEmailDomain(extractEmailDomain(rawEmail))) {
@@ -217,13 +234,14 @@ async function registerAccount(
 		discriminator = await allocateDiscriminator(discriminatorService, usernameCandidate);
 	}
 	const username = usernameCandidate!;
-	const grantBootstrapAdmin =
+	const bootstrapAdminEligible =
 		shouldAttemptBootstrapAdminGrant(config, {
 			rawEmail,
 			hasPassword: Boolean(data.password),
 			usernameMode,
 			pendingApproval: registrationAccess.pendingApproval,
 			setupConfigured: appPublicConfig.setup.configured,
+			setupTokenVerified,
 		}) && !(await instanceConfigRepository.isAdminBootstrapped());
 	if (
 		profileSubstringBlocklistCache.containsBannedSubstring('username', username) ||
@@ -258,7 +276,7 @@ async function registerAccount(
 		privacy_agreed_at: requiresPrivacyConsent ? now : null,
 		last_active_at: now,
 		last_active_ip: clientIp,
-		acls: grantBootstrapAdmin ? new Set([AdminACLs.WILDCARD]) : null,
+		acls: null,
 		traits: registrationAccess.pendingApproval ? new Set([REGISTRATION_PENDING_APPROVAL_TRAIT]) : null,
 		version: 1,
 	};
@@ -269,6 +287,7 @@ async function registerAccount(
 	);
 	let user: User;
 	let createAttempted = false;
+	let grantBootstrapAdmin = false;
 	let usernameReservation: UsernameReservation | null = null;
 	try {
 		if (uniqueUsernames) {
@@ -286,8 +305,9 @@ async function registerAccount(
 				client_ip: clientIp,
 			});
 		}
+		grantBootstrapAdmin = bootstrapAdminEligible && (await instanceConfigRepository.claimAdminBootstrap(userId));
 		createAttempted = true;
-		user = await users.create(userRow);
+		user = await users.create(grantBootstrapAdmin ? {...userRow, acls: new Set([AdminACLs.WILDCARD])} : userRow);
 	} catch (error) {
 		if (!createAttempted) {
 			await withdrawSignupOfUncreatedAccount(instanceConfigRepository, {
@@ -295,11 +315,16 @@ async function registerAccount(
 				registrationUrlUse,
 				pendingApproval: registrationAccess.pendingApproval,
 			});
+		} else if (grantBootstrapAdmin) {
+			await releaseBootstrapAdminOfUncreatedAccount(instanceConfigRepository, userId);
 		}
 		throw error;
 	} finally {
 		await usernameReservation?.release();
 	}
+	if (grantBootstrapAdmin) {
+		await clearUsedSetupToken(instanceConfigRepository);
+	}
 	await users.upsertSettings(
 		UserSettings.getDefaultUserSettings({
 			userId,
@@ -348,9 +373,6 @@ async function registerAccount(
 		user,
 		origin: AuthSession.resolveSessionOrigin(ctx, request),
 	});
-	if (grantBootstrapAdmin) {
-		await instanceConfigRepository.markAdminBootstrapped();
-	}
 	return {
 		user_id: user.id.toString(),
 		token,
@@ -365,11 +387,13 @@ function shouldAttemptBootstrapAdminGrant(
 		usernameMode: boolean;
 		pendingApproval: boolean;
 		setupConfigured: boolean;
+		setupTokenVerified: boolean;
 	},
 ): boolean {
+	const claimedAccount = params.usernameMode ? params.hasPassword : params.rawEmail !== null;
+	if (isSetupTokenEnforced(config)) return params.setupTokenVerified && claimedAccount;
 	const localDevInstance = config.nodeEnv === 'development' && !config.dev.testModeEnabled;
 	const setupBootstrapOpen = !params.setupConfigured;
-	const claimedAccount = params.usernameMode ? params.hasPassword : params.rawEmail !== null;
 	return (
 		(config.instance.selfHosted || localDevInstance || setupBootstrapOpen) && claimedAccount && !params.pendingApproval
 	);
@@ -432,6 +456,20 @@ async function withdrawSignupOfUncreatedAccount(
 	}
 }

+async function releaseBootstrapAdminOfUncreatedAccount(
+	instanceConfigRepository: InstanceConfigRepository,
+	userId: UserID,
+): Promise<void> {
+	try {
+		await instanceConfigRepository.releaseAdminBootstrap();
+	} catch (error) {
+		Logger.error(
+			{userId: userId.toString(), error},
+			'[AuthRegistration] Failed to release the admin bootstrap claim of an account that was never created',
+		);
+	}
+}
+
 async function resolveRegistrationAccess(
 	instanceConfigRepository: InstanceConfigRepository,
 	registrationUrlCode: string | null | undefined,
@@ -12,7 +12,8 @@ import {
 import type {ApiTestHarness} from '@app/api/test/ApiTestHarness';
 import {generateUniquePassword, HTTP_STATUS} from '@app/api/test/TestConstants';
 import {createBuilder, createBuilderWithoutAuth} from '@app/api/test/TestRequestBuilder';
-import {afterAll, beforeAll, beforeEach, describe, expect, it} from 'vitest';
+import {UserRepository} from '@app/api/user/repositories/UserRepository';
+import {afterAll, beforeAll, beforeEach, describe, expect, it, vi} from 'vitest';

 describe('Password reset flow', () => {
 	let harness: ApiTestHarness;
@@ -104,6 +105,61 @@ describe('Password reset flow', () => {
 		const login = await loginUser(harness, {email: account.email, password: newPassword});
 		expect('token' in login && login.token.length > 0).toBe(true);
 	});
+	it('accepts a reset token for only one of several concurrent resets', async () => {
+		const account = await createTestAccount(harness);
+		await createBuilderWithoutAuth(harness)
+			.post('/auth/forgot')
+			.body({email: account.email})
+			.expect(HTTP_STATUS.NO_CONTENT)
+			.execute();
+		const emails = await listTestEmails(harness, {recipient: account.email});
+		const token = findLastTestEmail(emails, 'password_reset')!.metadata!.token!;
+		const results = await Promise.all(
+			Array.from({length: 4}, () =>
+				createBuilderWithoutAuth(harness)
+					.post('/auth/reset')
+					.body({token, password: generateUniquePassword()})
+					.executeRaw(),
+			),
+		);
+		const statuses = results.map(({response}) => response.status).sort();
+		expect(statuses).toEqual(
+			[HTTP_STATUS.OK, HTTP_STATUS.BAD_REQUEST, HTTP_STATUS.BAD_REQUEST, HTTP_STATUS.BAD_REQUEST].sort(),
+		);
+	});
+	it('keeps a reset token usable when the reset fails before the password is written', async () => {
+		const account = await createTestAccount(harness);
+		await createBuilderWithoutAuth(harness)
+			.post('/auth/forgot')
+			.body({email: account.email})
+			.expect(HTTP_STATUS.NO_CONTENT)
+			.execute();
+		const emails = await listTestEmails(harness, {recipient: account.email});
+		const token = findLastTestEmail(emails, 'password_reset')!.metadata!.token!;
+		const patchUpsert = vi
+			.spyOn(UserRepository.prototype, 'patchUpsert')
+			.mockRejectedValueOnce(new Error('the user row write failed'));
+		try {
+			await createBuilderWithoutAuth(harness)
+				.post('/auth/reset')
+				.body({token, password: generateUniquePassword()})
+				.expect(HTTP_STATUS.INTERNAL_SERVER_ERROR)
+				.execute();
+		} finally {
+			patchUpsert.mockRestore();
+		}
+		const newPassword = generateUniquePassword();
+		const resetResp = await createBuilderWithoutAuth<LoginSuccessResponse>(harness)
+			.post('/auth/reset')
+			.body({token, password: newPassword})
+			.execute();
+		expect(resetResp.token.length).toBeGreaterThan(0);
+		await createBuilderWithoutAuth(harness)
+			.post('/auth/reset')
+			.body({token, password: generateUniquePassword()})
+			.expect(HTTP_STATUS.BAD_REQUEST)
+			.execute();
+	});
 	it('rejects invalid reset token', async () => {
 		await createTestAccount(harness);
 		await createBuilderWithoutAuth(harness)
@@ -14,11 +14,19 @@ import {
 import {createUserID} from '@app/api/BrandedTypes';
 import {getConfig} from '@app/api/Config';
 import {applySharedListUpdate, resetSharedListsForTests} from '@app/api/infrastructure/activity/SharedLists';
-import {getInstanceConfigRepository, getUserRepository} from '@app/api/middleware/ServiceSingletons';
+import {
+	getInstanceConfigRepository,
+	getRateLimitService,
+	getUserRepository,
+} from '@app/api/middleware/ServiceSingletons';
 import type {ApiTestHarness} from '@app/api/test/ApiTestHarness';
+import {HTTP_STATUS} from '@app/api/test/TestConstants';
 import {createBuilder, createBuilderWithoutAuth} from '@app/api/test/TestRequestBuilder';
 import {AdminACLs} from '@fluxer/constants/src/AdminACLs';
-import {afterAll, beforeAll, beforeEach, describe, expect, it} from 'vitest';
+import {ValidationErrorCodes} from '@fluxer/constants/src/ValidationErrorCodes';
+import {getSameIpDecisionKey} from '@fluxer/ip_utils/src/IpAddress';
+import {ms} from 'itty-time';
+import {afterAll, beforeAll, beforeEach, describe, expect, it, vi} from 'vitest';

 function bootstrapRegistrationBody(prefix: string): Record<string, unknown> {
 	return {
@@ -57,6 +65,37 @@ async function withBootstrapAdminConfig(
 	}
 }

+const SETUP_TOKEN = 'setup-token-for-tests-0123456789-abcdefghijklmnopqrstuvwxyz';
+const WRONG_SETUP_TOKEN = 'wrong-setup-token-0123456789-abcdefghijklmnopqrstuvwxyz';
+const SETUP_TOKEN_HASH_KEY = 'setup_token_hash';
+const TOO_MANY_REQUESTS = 429;
+
+interface SetupTokenRegistrationResponse {
+	user_id?: string;
+	token?: string;
+	registration_pending_approval?: boolean;
+	code?: string;
+	errors?: Array<{path: string; code: string}>;
+}
+
+async function withSetupTokenInstance(callback: () => Promise<void>): Promise<void> {
+	const config = getConfig();
+	const originalSelfHosted = config.instance.selfHosted;
+	const originalSetupToken = config.instance.setup.token;
+	const originalSetupConfigured = config.instance.setup.configured;
+	const originalRelaxRegistrationRateLimits = config.dev.relaxRegistrationRateLimits;
+	try {
+		config.instance.selfHosted = true;
+		config.instance.setup.token = SETUP_TOKEN;
+		await callback();
+	} finally {
+		config.instance.selfHosted = originalSelfHosted;
+		config.instance.setup.token = originalSetupToken;
+		config.instance.setup.configured = originalSetupConfigured;
+		config.dev.relaxRegistrationRateLimits = originalRelaxRegistrationRateLimits;
+	}
+}
+
 async function expectUserACLs(userId: string, expectedACLs: Array<string>): Promise<void> {
 	const user = await getUserRepository().findUniqueAssert(createUserID(BigInt(userId)));
 	expect([...user.acls].sort()).toEqual([...expectedACLs].sort());
@@ -123,31 +162,45 @@ describe('Auth registration', () => {
 			await expect(getInstanceConfigRepository().isAdminBootstrapped()).resolves.toBe(true);
 		});
 	});
-	it('allows setup-open sessions to fetch instance config when bootstrap marker is stale', async () => {
+	it('lets exactly one concurrent caller claim the admin bootstrap', async () => {
+		const instanceConfigRepository = getInstanceConfigRepository();
+		const claims = await Promise.all(Array.from({length: 5}, () => instanceConfigRepository.claimAdminBootstrap()));
+		expect(claims.filter(Boolean)).toHaveLength(1);
+		await expect(instanceConfigRepository.isAdminBootstrapped()).resolves.toBe(true);
+		await expect(instanceConfigRepository.claimAdminBootstrap()).resolves.toBe(false);
+	});
+	it('keeps instance config closed to sessions without admin ACLs while setup is open', async () => {
 		await withBootstrapAdminConfig({selfHosted: false, testModeEnabled: true}, async () => {
 			const instanceConfigRepository = getInstanceConfigRepository();
 			await instanceConfigRepository.setAppPublicConfig({setup: {configured: false}});
-			await instanceConfigRepository.markAdminBootstrapped();
-			const account = await registerUser(harness, bootstrapRegistrationBody('stalesetupmarker'));
+			await instanceConfigRepository.claimAdminBootstrap();
+			const account = await registerUser(harness, bootstrapRegistrationBody('setupopennonadmin'));
 			await expectUserACLs(account.user_id, []);
-			await createBuilder(harness, account.token).get('/admin/instance/config').execute();
+			await createBuilder(harness, account.token).get('/admin/instance/config').expect(HTTP_STATUS.FORBIDDEN).execute();
+			await createBuilder(harness, account.token)
+				.patch('/admin/instance/config')
+				.body({app_public: {setup: {configured: true}}})
+				.expect(HTTP_STATUS.FORBIDDEN)
+				.execute();
+			await expectUserACLs(account.user_id, []);
+			await expect(instanceConfigRepository.getAppPublicConfig()).resolves.toMatchObject({
+				setup: {configured: false},
+			});
 		});
 	});
-	it('repairs setup completer admin ACL when bootstrap marker is stale', async () => {
+	it('lets the bootstrap admin complete setup', async () => {
 		await withBootstrapAdminConfig({selfHosted: false, testModeEnabled: true}, async () => {
 			const instanceConfigRepository = getInstanceConfigRepository();
 			await instanceConfigRepository.setAppPublicConfig({setup: {configured: false}});
-			await instanceConfigRepository.markAdminBootstrapped();
-			const account = await registerUser(harness, bootstrapRegistrationBody('stalesetupcomplete'));
-			await expectUserACLs(account.user_id, []);
-
+			const account = await registerUser(harness, bootstrapRegistrationBody('setupopenowner'));
+			await expectUserACLs(account.user_id, [AdminACLs.WILDCARD]);
 			await createBuilder(harness, account.token)
 				.patch('/admin/instance/config')
 				.body({app_public: {setup: {configured: true}}})
 				.execute();
-
-			await expectUserACLs(account.user_id, [AdminACLs.WILDCARD]);
-			await createBuilder(harness, account.token).get('/admin/instance/config').execute();
+			await expect(instanceConfigRepository.getAppPublicConfig()).resolves.toMatchObject({
+				setup: {configured: true},
+			});
 		});
 	});
 	it('derives username from display name when username is omitted', async () => {
@@ -237,3 +290,303 @@ describe('Auth registration', () => {
 		expect(me.email).toBe('[email protected]');
 	});
 });
+
+describe('Setup token registration', () => {
+	let harness: ApiTestHarness;
+	beforeAll(async () => {
+		harness = await createAuthHarness();
+	});
+	beforeEach(async () => {
+		await harness.reset();
+	});
+	afterAll(async () => {
+		await harness?.shutdown();
+	});
+
+	async function register(
+		body: Record<string, unknown>,
+		ipAddress?: string,
+	): Promise<{status: number; json: SetupTokenRegistrationResponse}> {
+		const builder = createBuilderWithoutAuth<SetupTokenRegistrationResponse>(harness).post('/auth/register').body(body);
+		if (ipAddress) builder.header('x-forwarded-for', ipAddress);
+		const {response, json} = await builder.executeRaw();
+		return {status: response.status, json};
+	}
+
+	function setupTokenErrors(json: SetupTokenRegistrationResponse): Array<{path: string; code: string}> {
+		return (json.errors ?? []).map(({path, code}) => ({path, code}));
+	}
+
+	async function registerAdmin(prefix: string, ipAddress?: string): Promise<string> {
+		const {status, json} = await register({...bootstrapRegistrationBody(prefix), setup_token: SETUP_TOKEN}, ipAddress);
+		expect(status).toBe(HTTP_STATUS.OK);
+		return json.user_id!;
+	}
+
+	it('refuses a registration that sends no setup token', async () => {
+		await withSetupTokenInstance(async () => {
+			const body = bootstrapRegistrationBody('tokenless');
+			const {status, json} = await register(body);
+			expect(status).toBe(HTTP_STATUS.BAD_REQUEST);
+			expect(setupTokenErrors(json)).toEqual([{path: 'setup_token', code: ValidationErrorCodes.SETUP_TOKEN_REQUIRED}]);
+			expect(await getUserRepository().findByEmail(body.email as string)).toBeNull();
+			await expect(getInstanceConfigRepository().isAdminBootstrapped()).resolves.toBe(false);
+		});
+	});
+
+	it('refuses a registration that sends a wrong setup token', async () => {
+		await withSetupTokenInstance(async () => {
+			const body = bootstrapRegistrationBody('wrongtoken');
+			const {status, json} = await register({...body, setup_token: WRONG_SETUP_TOKEN});
+			expect(status).toBe(HTTP_STATUS.BAD_REQUEST);
+			expect(setupTokenErrors(json)).toEqual([{path: 'setup_token', code: ValidationErrorCodes.SETUP_TOKEN_INVALID}]);
+			expect(await getUserRepository().findByEmail(body.email as string)).toBeNull();
+			await expect(getInstanceConfigRepository().isAdminBootstrapped()).resolves.toBe(false);
+		});
+	});
+
+	it('makes the registration that presents the setup token the admin', async () => {
+		await withSetupTokenInstance(async () => {
+			const userId = await registerAdmin('tokenadmin');
+			await expectUserACLs(userId, [AdminACLs.WILDCARD]);
+			await expect(getInstanceConfigRepository().isAdminBootstrapped()).resolves.toBe(true);
+			expect((await getInstanceConfigRepository().getConfig(SETUP_TOKEN_HASH_KEY)) ?? '').toBe('');
+		});
+	});
+
+	it('accepts a setup token padded with whitespace', async () => {
+		await withSetupTokenInstance(async () => {
+			const {status, json} = await register({
+				...bootstrapRegistrationBody('paddedtoken'),
+				setup_token: `  ${SETUP_TOKEN}\n`,
+			});
+			expect(status).toBe(HTTP_STATUS.OK);
+			await expectUserACLs(json.user_id!, [AdminACLs.WILDCARD]);
+		});
+	});
+
+	it('ignores the setup token once the admin exists', async () => {
+		await withSetupTokenInstance(async () => {
+			await registerAdmin('firstadmin');
+			const tokenless = await register(bootstrapRegistrationBody('aftertokenless'));
+			expect(tokenless.status).toBe(HTTP_STATUS.OK);
+			await expectUserACLs(tokenless.json.user_id!, []);
+			const wrong = await register({...bootstrapRegistrationBody('afterwrong'), setup_token: WRONG_SETUP_TOKEN});
+			expect(wrong.status).toBe(HTTP_STATUS.OK);
+			await expectUserACLs(wrong.json.user_id!, []);
+			const repeated = await register({...bootstrapRegistrationBody('afterrepeat'), setup_token: SETUP_TOKEN});
+			expect(repeated.status).toBe(HTTP_STATUS.OK);
+			await expectUserACLs(repeated.json.user_id!, []);
+		});
+	});
+
+	it('refuses an unclaimed registration that sends no setup token', async () => {
+		await withSetupTokenInstance(async () => {
+			const {status, json} = await register({global_name: 'Unclaimed Visitor'});
+			expect(status).toBe(HTTP_STATUS.BAD_REQUEST);
+			expect(setupTokenErrors(json)).toEqual([{path: 'setup_token', code: ValidationErrorCodes.SETUP_TOKEN_REQUIRED}]);
+		});
+	});
+
+	it('creates a plain account for an unclaimed registration that presents the setup token', async () => {
+		await withSetupTokenInstance(async () => {
+			const {status, json} = await register({global_name: 'Unclaimed Operator', setup_token: SETUP_TOKEN});
+			expect(status).toBe(HTTP_STATUS.OK);
+			await expectUserACLs(json.user_id!, []);
+			await expect(getInstanceConfigRepository().isAdminBootstrapped()).resolves.toBe(false);
+			const userId = await registerAdmin('claimedoperator');
+			await expectUserACLs(userId, [AdminACLs.WILDCARD]);
+		});
+	});
+
+	it.each(['approval', 'closed'] as const)(
+		'lets the setup token holder register as admin while registration is %s',
+		async (mode) => {
+			await withSetupTokenInstance(async () => {
+				await getInstanceConfigRepository().setRegistrationConfig({mode});
+				const {status, json} = await register({...bootstrapRegistrationBody(`mode${mode}`), setup_token: SETUP_TOKEN});
+				expect(status).toBe(HTTP_STATUS.OK);
+				expect(json.registration_pending_approval).toBeUndefined();
+				expect(json.token).toBeTruthy();
+				await expectUserACLs(json.user_id!, [AdminACLs.WILDCARD]);
+				await expect(getInstanceConfigRepository().getPendingRegistrations()).resolves.toEqual([]);
+			});
+		},
+	);
+
+	it('reports the missing setup token before any other registration check', async () => {
+		await withSetupTokenInstance(async () => {
+			await getInstanceConfigRepository().setAppPublicConfig({legal: {terms_url: 'https://example.com/terms'}});
+			const body = {...bootstrapRegistrationBody('noconsent'), consent: false};
+			const tokenless = await register(body);
+			expect(tokenless.status).toBe(HTTP_STATUS.BAD_REQUEST);
+			expect(setupTokenErrors(tokenless.json)).toEqual([
+				{path: 'setup_token', code: ValidationErrorCodes.SETUP_TOKEN_REQUIRED},
+			]);
+			const verified = await register({...body, setup_token: SETUP_TOKEN});
+			expect(verified.status).toBe(HTTP_STATUS.BAD_REQUEST);
+			expect(setupTokenErrors(verified.json)).toEqual([
+				{path: 'consent', code: ValidationErrorCodes.MUST_AGREE_TO_TOS_AND_PRIVACY_POLICY},
+			]);
+			await expect(getInstanceConfigRepository().isAdminBootstrapped()).resolves.toBe(false);
+		});
+	});
+
+	it('locks an address out after ten wrong setup tokens', async () => {
+		await withSetupTokenInstance(async () => {
+			getConfig().dev.relaxRegistrationRateLimits = false;
+			const attacker = '203.0.113.10';
+			const operator = '203.0.113.20';
+			for (let attempt = 0; attempt < 3; attempt++) {
+				const tokenless = await register(bootstrapRegistrationBody(`limitmissing${attempt}`), attacker);
+				expect(setupTokenErrors(tokenless.json)).toEqual([
+					{path: 'setup_token', code: ValidationErrorCodes.SETUP_TOKEN_REQUIRED},
+				]);
+			}
+			for (let attempt = 0; attempt < 10; attempt++) {
+				const wrong = await register(
+					{...bootstrapRegistrationBody(`limitwrong${attempt}`), setup_token: WRONG_SETUP_TOKEN},
+					attacker,
+				);
+				expect(wrong.status).toBe(HTTP_STATUS.BAD_REQUEST);
+				expect(setupTokenErrors(wrong.json)).toEqual([
+					{path: 'setup_token', code: ValidationErrorCodes.SETUP_TOKEN_INVALID},
+				]);
+			}
+			const eleventh = await register(
+				{...bootstrapRegistrationBody('limiteleventh'), setup_token: WRONG_SETUP_TOKEN},
+				attacker,
+			);
+			expect(eleventh.status).toBe(TOO_MANY_REQUESTS);
+			const lockedOut = await register(
+				{...bootstrapRegistrationBody('limitlocked'), setup_token: SETUP_TOKEN},
+				attacker,
+			);
+			expect(lockedOut.status).toBe(TOO_MANY_REQUESTS);
+			await expect(getInstanceConfigRepository().isAdminBootstrapped()).resolves.toBe(false);
+			const userId = await registerAdmin('limitoperator', operator);
+			await expectUserACLs(userId, [AdminACLs.WILDCARD]);
+		});
+	});
+
+	it('lets the setup token holder past the registration limiter of their address', async () => {
+		await withSetupTokenInstance(async () => {
+			getConfig().dev.relaxRegistrationRateLimits = false;
+			const operator = '203.0.113.30';
+			const registrationLimit = {
+				identifier: `registration:ip:${getSameIpDecisionKey(operator) ?? operator}`,
+				maxAttempts: 3,
+				windowMs: ms('1 hour'),
+			};
+			for (let attempt = 0; attempt < 3; attempt++) {
+				await getRateLimitService().checkLimit(registrationLimit);
+			}
+			const userId = await registerAdmin('limitedoperator', operator);
+			await expectUserACLs(userId, [AdminACLs.WILDCARD]);
+			const next = await register(bootstrapRegistrationBody('limitedmember'), operator);
+			expect(next.status).toBe(TOO_MANY_REQUESTS);
+		});
+	});
+
+	it('ties the admin grant to the setup token on an instance configured through the environment', async () => {
+		await withSetupTokenInstance(async () => {
+			getConfig().instance.setup.configured = true;
+			const tokenless = await register(bootstrapRegistrationBody('envtokenless'));
+			expect(tokenless.status).toBe(HTTP_STATUS.OK);
+			await expectUserACLs(tokenless.json.user_id!, []);
+			await expect(getInstanceConfigRepository().isAdminBootstrapped()).resolves.toBe(false);
+			const wrong = await register({...bootstrapRegistrationBody('envwrong'), setup_token: WRONG_SETUP_TOKEN});
+			expect(wrong.status).toBe(HTTP_STATUS.BAD_REQUEST);
+			expect(setupTokenErrors(wrong.json)).toEqual([
+				{path: 'setup_token', code: ValidationErrorCodes.SETUP_TOKEN_INVALID},
+			]);
+			const userId = await registerAdmin('envadmin');
+			await expectUserACLs(userId, [AdminACLs.WILDCARD]);
+			await expect(getInstanceConfigRepository().isAdminBootstrapped()).resolves.toBe(true);
+		});
+	});
+
+	it('ties the admin grant to the setup token on an instance configured in storage', async () => {
+		await withSetupTokenInstance(async () => {
+			await getInstanceConfigRepository().setAppPublicConfig({setup: {configured: true}});
+			const tokenless = await register(bootstrapRegistrationBody('storedtokenless'));
+			expect(tokenless.status).toBe(HTTP_STATUS.OK);
+			await expectUserACLs(tokenless.json.user_id!, []);
+			const userId = await registerAdmin('storedadmin');
+			await expectUserACLs(userId, [AdminACLs.WILDCARD]);
+		});
+	});
+
+	it('leaves the hosted service alone even with a setup token configured', async () => {
+		await withSetupTokenInstance(async () => {
+			getConfig().instance.selfHosted = false;
+			await getInstanceConfigRepository().setAppPublicConfig({setup: {configured: false}});
+			const {status, json} = await register(bootstrapRegistrationBody('hostedtokenless'));
+			expect(status).toBe(HTTP_STATUS.OK);
+			await expectUserACLs(json.user_id!, [AdminACLs.WILDCARD]);
+		});
+	});
+
+	it('releases the admin claim when the account cannot be created', async () => {
+		await withSetupTokenInstance(async () => {
+			const create = vi.spyOn(getUserRepository(), 'create').mockRejectedValueOnce(new Error('insert failed'));
+			try {
+				const failed = await register({...bootstrapRegistrationBody('failedadmin'), setup_token: SETUP_TOKEN});
+				expect(failed.status).toBe(HTTP_STATUS.INTERNAL_SERVER_ERROR);
+				expect(create).toHaveBeenCalledTimes(1);
+			} finally {
+				create.mockRestore();
+			}
+			await expect(getInstanceConfigRepository().isAdminBootstrapped()).resolves.toBe(false);
+			const tokenless = await register(bootstrapRegistrationBody('failedtokenless'));
+			expect(setupTokenErrors(tokenless.json)).toEqual([
+				{path: 'setup_token', code: ValidationErrorCodes.SETUP_TOKEN_REQUIRED},
+			]);
+			const userId = await registerAdmin('retriedadmin');
+			await expectUserACLs(userId, [AdminACLs.WILDCARD]);
+			await expect(getInstanceConfigRepository().getConfig('admin_bootstrap_user_id')).resolves.toBe(userId);
+		});
+	});
+
+	it('burns a generated setup token once the admin exists', async () => {
+		await withSetupTokenInstance(async () => {
+			const config = getConfig();
+			const originalNodeEnv = config.nodeEnv;
+			config.instance.setup.token = null;
+			config.nodeEnv = 'production';
+			try {
+				const repository = getInstanceConfigRepository();
+				const generated = await repository.createSetupTokenIfAbsent();
+				expect(generated).not.toBeNull();
+				const wrong = await register({...bootstrapRegistrationBody('genwrong'), setup_token: SETUP_TOKEN});
+				expect(setupTokenErrors(wrong.json)).toEqual([
+					{path: 'setup_token', code: ValidationErrorCodes.SETUP_TOKEN_INVALID},
+				]);
+				const {status, json} = await register({...bootstrapRegistrationBody('genadmin'), setup_token: generated});
+				expect(status).toBe(HTTP_STATUS.OK);
+				await expectUserACLs(json.user_id!, [AdminACLs.WILDCARD]);
+				expect(await repository.getConfig(SETUP_TOKEN_HASH_KEY)).toBe('');
+				await expect(repository.verifySetupToken(generated)).resolves.toBe(false);
+			} finally {
+				config.nodeEnv = originalNodeEnv;
+			}
+		});
+	});
+
+	it('burns the stored setup token when an admin marks setup as configured', async () => {
+		await withBootstrapAdminConfig({selfHosted: false, testModeEnabled: true}, async () => {
+			const repository = getInstanceConfigRepository();
+			await repository.setAppPublicConfig({setup: {configured: false}});
+			const account = await registerUser(harness, bootstrapRegistrationBody('configuringadmin'));
+			await repository.releaseAdminBootstrap();
+			const generated = await repository.createSetupTokenIfAbsent();
+			await expect(repository.verifySetupToken(generated)).resolves.toBe(true);
+			await createBuilder(harness, account.token)
+				.patch('/admin/instance/config')
+				.body({app_public: {setup: {configured: true}}})
+				.execute();
+			await expect(repository.isAdminBootstrapped()).resolves.toBe(true);
+			await expect(repository.verifySetupToken(generated)).resolves.toBe(false);
+		});
+	});
+});
@@ -283,6 +283,7 @@ export interface APIConfig {
 		};
 		setup: {
 			configured: boolean;
+			token: string | null;
 		};
 		accountIdentity: AccountIdentityMode | null;
 		tagStyle: TagStyle | null;
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later

 import {createHash} from 'node:crypto';
+import {createUserID} from '@app/api/BrandedTypes';
 import {Config, getConfig} from '@app/api/Config';
 import type {CassandraQueryExecutorForTesting} from '@app/api/database/CassandraQueryExecution';
 import {setCassandraQueryExecutorForTesting} from '@app/api/database/CassandraQueryExecution';
@@ -14,6 +15,7 @@ import {
 } from '@app/api/instance/InstanceConfigRepository';
 import {getLegalUrls, setCachedConfiguredLegalUrls} from '@app/api/instance/LegalUrls';
 import {getInstanceProductName, setCachedProductName} from '@app/api/instance/ProductName';
+import {ensureSetupToken, isSetupTokenEnforced} from '@app/api/instance/SetupToken';
 import {InstanceConfigWriteRaceExecutor} from '@app/api/instance/tests/InstanceConfigWriteRaceExecutor';
 import {dockerAvailable, startPostgresKv, stopPostgresKv} from '@app/api/test/DockerTestContainer';
 import {InMemoryCassandraQueryExecutor} from '@app/api/test/InMemoryCassandraQueryExecutor';
@@ -38,6 +40,8 @@ const REGISTRATION_CONFIG_KEY = 'registration_config';
 const REGISTRATION_URLS_KEY = 'registration_urls';
 const REGISTRATION_PENDING_APPROVALS_KEY = 'registration_pending_approvals';
 const POSTGRES_KV_TABLE = 'kv_instance_config_races';
+const SETUP_TOKEN_HASH_KEY = 'setup_token_hash';
+const ENV_SETUP_TOKEN = 'setup-token-for-tests-0123456789-abcdefghijklmnopqrstuvwxyz';
 describe('InstanceConfigRepository', () => {
 	const repositories: Array<InstanceConfigRepository> = [];

@@ -945,6 +949,271 @@ function registrationUrlParams(maxUses: number | null) {
 	};
 }

+describe('InstanceConfigRepository setup token', () => {
+	const repositories: Array<InstanceConfigRepository> = [];
+	const config = getConfig();
+	let executor: InstanceConfigWriteRaceExecutor;
+	let kvProvider: MockKVProvider;
+	let originalSelfHosted: boolean;
+	let originalNodeEnv: typeof config.nodeEnv;
+	let originalSetupToken: typeof config.instance.setup.token;
+	let originalSetupConfigured: boolean;
+
+	beforeEach(() => {
+		executor = new InstanceConfigWriteRaceExecutor(new InMemoryCassandraQueryExecutor());
+		setCassandraQueryExecutorForTesting(executor);
+		kvProvider = new MockKVProvider();
+		originalSelfHosted = config.instance.selfHosted;
+		originalNodeEnv = config.nodeEnv;
+		originalSetupToken = config.instance.setup.token;
+		originalSetupConfigured = config.instance.setup.configured;
+	});
+
+	afterEach(() => {
+		config.instance.selfHosted = originalSelfHosted;
+		config.nodeEnv = originalNodeEnv;
+		config.instance.setup.token = originalSetupToken;
+		config.instance.setup.configured = originalSetupConfigured;
+		for (const repository of repositories) {
+			repository.shutdown();
+		}
+		repositories.length = 0;
+		setCassandraQueryExecutorForTesting(new InMemoryCassandraQueryExecutor());
+	});
+
+	function createPod(): InstanceConfigRepository {
+		const repository = new InstanceConfigRepository(kvProvider);
+		repositories.push(repository);
+		return repository;
+	}
+
+	function useSelfHostedProduction(): void {
+		config.instance.selfHosted = true;
+		config.nodeEnv = 'production';
+		config.instance.setup.token = null;
+		config.instance.setup.configured = false;
+	}
+
+	function sha256(value: string): string {
+		return createHash('sha256').update(value).digest('hex');
+	}
+
+	const accountExists = async () => true;
+	const accountMissing = async () => false;
+
+	it('generates one setup token when two pods start together and stores only its hash', async () => {
+		const tokens = await Promise.all([createPod().createSetupTokenIfAbsent(), createPod().createSetupTokenIfAbsent()]);
+		const generated = tokens.filter((token) => token !== null);
+		expect(generated).toHaveLength(1);
+		expect(tokens.filter((token) => token === null)).toHaveLength(1);
+		const stored = await executor.readDirectly(SETUP_TOKEN_HASH_KEY);
+		expect(stored).toBe(sha256(generated[0]!));
+		expect(stored).not.toBe(generated[0]);
+		expect(await createPod().createSetupTokenIfAbsent()).toBeNull();
+	});
+
+	it('verifies only the generated setup token', async () => {
+		const pod = createPod();
+		for (const presented of ['anything', '', null, undefined]) {
+			expect(await pod.verifySetupToken(presented)).toBe(false);
+		}
+		const token = await pod.createSetupTokenIfAbsent();
+		expect(await pod.verifySetupToken(token)).toBe(true);
+		expect(await createPod().verifySetupToken(token)).toBe(true);
+		for (const presented of [`${token}x`, sha256(token!), '', null, undefined]) {
+			expect(await pod.verifySetupToken(presented)).toBe(false);
+		}
+	});
+
+	it('takes the environment setup token over a generated one', async () => {
+		const pod = createPod();
+		const generated = await pod.createSetupTokenIfAbsent();
+		config.instance.setup.token = ENV_SETUP_TOKEN;
+		expect(await pod.verifySetupToken(ENV_SETUP_TOKEN)).toBe(true);
+		expect(await pod.verifySetupToken(generated)).toBe(false);
+		expect(await executor.readDirectly(SETUP_TOKEN_HASH_KEY)).toBe(sha256(generated!));
+	});
+
+	it('burns the stored setup token and leaves it alone when the admin bootstrap is only claimed', async () => {
+		useSelfHostedProduction();
+		const pod = createPod();
+		const token = await pod.createSetupTokenIfAbsent();
+		await pod.claimAdminBootstrap();
+		expect(await executor.readDirectly(SETUP_TOKEN_HASH_KEY)).toBe(sha256(token!));
+		await pod.burnSetupToken();
+		expect(await executor.readDirectly(SETUP_TOKEN_HASH_KEY)).toBe('');
+		expect(await pod.verifySetupToken(token)).toBe(false);
+		expect(await pod.verifySetupToken('')).toBe(false);
+		await ensureSetupToken(pod, accountExists);
+		expect(await executor.readDirectly(SETUP_TOKEN_HASH_KEY)).toBe('');
+	});
+
+	it('writes nothing when there is no stored setup token to burn', async () => {
+		await createPod().burnSetupToken();
+		expect(await executor.readDirectly(SETUP_TOKEN_HASH_KEY)).toBeNull();
+	});
+
+	it('releases a claimed admin bootstrap so it can be claimed again', async () => {
+		const pod = createPod();
+		await pod.releaseAdminBootstrap();
+		expect(await executor.readDirectly('admin_bootstrapped')).toBeNull();
+		expect(await pod.claimAdminBootstrap()).toBe(true);
+		expect(await pod.isAdminBootstrapped()).toBe(true);
+		await pod.releaseAdminBootstrap();
+		expect(await pod.isAdminBootstrapped()).toBe(false);
+		expect(await createPod().isAdminBootstrapped()).toBe(false);
+		expect(await pod.claimAdminBootstrap()).toBe(true);
+		expect(await pod.claimAdminBootstrap()).toBe(false);
+	});
+
+	it('keeps a won admin bootstrap claim when the refresh cannot be published', async () => {
+		const pod = createPod();
+		await pod.isAdminBootstrapped();
+		vi.spyOn(kvProvider, 'publish').mockRejectedValueOnce(new Error('kv down'));
+		expect(await pod.claimAdminBootstrap()).toBe(true);
+		expect(await pod.isAdminBootstrapped()).toBe(true);
+		expect(await executor.readDirectly('admin_bootstrapped')).toBe('true');
+	});
+
+	it('enforces the setup token only on self-hosted instances that run in production or configure one', async () => {
+		const pod = createPod();
+		const gate = async () => ({
+			enforced: isSetupTokenEnforced(config),
+			open: await pod.isSetupTokenGateOpen(),
+			required: await pod.isSetupTokenRequired(),
+		});
+		config.instance.setup.configured = false;
+		config.instance.selfHosted = false;
+		config.nodeEnv = 'production';
+		config.instance.setup.token = ENV_SETUP_TOKEN;
+		expect(await gate()).toEqual({enforced: false, open: false, required: false});
+		config.instance.selfHosted = true;
+		config.nodeEnv = 'development';
+		config.instance.setup.token = null;
+		expect(await gate()).toEqual({enforced: false, open: false, required: false});
+		config.instance.setup.token = ENV_SETUP_TOKEN;
+		expect(await gate()).toEqual({enforced: true, open: true, required: true});
+		config.nodeEnv = 'production';
+		config.instance.setup.token = null;
+		expect(await gate()).toEqual({enforced: true, open: true, required: true});
+		config.instance.setup.configured = true;
+		expect(await gate()).toEqual({enforced: true, open: true, required: false});
+		config.instance.setup.configured = false;
+		expect(await gate()).toEqual({enforced: true, open: true, required: true});
+		await pod.setAppPublicConfig({setup: {configured: true}});
+		expect(await gate()).toEqual({enforced: true, open: true, required: false});
+		await pod.claimAdminBootstrap();
+		expect(await gate()).toEqual({enforced: true, open: false, required: false});
+	});
+
+	it('stores a setup token on the first production start and keeps it on the next', async () => {
+		useSelfHostedProduction();
+		await ensureSetupToken(createPod(), accountExists);
+		const stored = await executor.readDirectly(SETUP_TOKEN_HASH_KEY);
+		expect(stored).toMatch(/^[a-f0-9]{64}$/);
+		await ensureSetupToken(createPod(), accountExists);
+		expect(await executor.readDirectly(SETUP_TOKEN_HASH_KEY)).toBe(stored);
+	});
+
+	it('stores a setup token when setup is configured but no admin exists', async () => {
+		useSelfHostedProduction();
+		config.instance.setup.configured = true;
+		await ensureSetupToken(createPod(), accountExists);
+		expect(await executor.readDirectly(SETUP_TOKEN_HASH_KEY)).toMatch(/^[a-f0-9]{64}$/);
+	});
+
+	it('stores no setup token when one is set in the environment', async () => {
+		useSelfHostedProduction();
+		config.instance.setup.token = ENV_SETUP_TOKEN;
+		await ensureSetupToken(createPod(), accountExists);
+		expect(await executor.readDirectly(SETUP_TOKEN_HASH_KEY)).toBeNull();
+	});
+
+	it('stores no setup token on the hosted service or in self-hosted development', async () => {
+		useSelfHostedProduction();
+		config.instance.selfHosted = false;
+		await ensureSetupToken(createPod(), accountExists);
+		config.instance.selfHosted = true;
+		config.nodeEnv = 'development';
+		await ensureSetupToken(createPod(), accountExists);
+		expect(await executor.readDirectly(SETUP_TOKEN_HASH_KEY)).toBeNull();
+	});
+
+	it('stores no setup token once the admin exists', async () => {
+		useSelfHostedProduction();
+		const pod = createPod();
+		await pod.claimAdminBootstrap();
+		await ensureSetupToken(pod, accountExists);
+		expect(await executor.readDirectly(SETUP_TOKEN_HASH_KEY)).toBeNull();
+	});
+
+	it('releases an admin bootstrap claim at start when the claiming account was never created', async () => {
+		useSelfHostedProduction();
+		const pod = createPod();
+		expect(await pod.claimAdminBootstrap(createUserID(4242n))).toBe(true);
+		expect(await executor.readDirectly('admin_bootstrap_user_id')).toBe('4242');
+		await ensureSetupToken(createPod(), accountExists);
+		expect(await executor.readDirectly('admin_bootstrapped')).toBe('true');
+		expect(await executor.readDirectly(SETUP_TOKEN_HASH_KEY)).toBeNull();
+		const restarted = createPod();
+		await ensureSetupToken(restarted, accountMissing);
+		expect(await executor.readDirectly('admin_bootstrapped')).toBe('false');
+		expect(await restarted.isSetupTokenGateOpen()).toBe(true);
+		expect(await executor.readDirectly(SETUP_TOKEN_HASH_KEY)).toMatch(/^[a-f0-9]{64}$/);
+	});
+
+	it('keeps an admin bootstrap claim at start when no claiming account is recorded', async () => {
+		useSelfHostedProduction();
+		const pod = createPod();
+		await pod.claimAdminBootstrap();
+		expect(await executor.readDirectly('admin_bootstrap_user_id')).toBeNull();
+		await ensureSetupToken(createPod(), accountMissing);
+		expect(await executor.readDirectly('admin_bootstrapped')).toBe('true');
+		await pod.releaseAdminBootstrap();
+		await pod.claimAdminBootstrap(createUserID(4242n));
+		await pod.releaseAdminBootstrap();
+		await pod.claimAdminBootstrap();
+		expect(await executor.readDirectly('admin_bootstrap_user_id')).toBe('');
+		await ensureSetupToken(createPod(), accountMissing);
+		expect(await executor.readDirectly('admin_bootstrapped')).toBe('true');
+	});
+
+	it('keeps a won admin bootstrap claim when the claiming account cannot be recorded', async () => {
+		const pod = createPod();
+		executor.watch('admin_bootstrap_user_id');
+		executor.competeBeforeEachWrite(async () => {
+			throw new Error('database down');
+		});
+		expect(await pod.claimAdminBootstrap(createUserID(4242n))).toBe(true);
+		expect(await pod.isAdminBootstrapped()).toBe(true);
+		expect(await executor.readDirectly('admin_bootstrapped')).toBe('true');
+		expect(await executor.readDirectly('admin_bootstrap_user_id')).toBeNull();
+	});
+
+	it('confirms the admin bootstrap against the database and repairs a stale snapshot', async () => {
+		const stale = createPod();
+		const writer = createPod();
+		expect(await stale.isAdminBootstrapped()).toBe(false);
+		vi.spyOn(kvProvider, 'publish').mockRejectedValueOnce(new Error('kv down'));
+		await writer.claimAdminBootstrap();
+		expect(await stale.isAdminBootstrapped()).toBe(false);
+		expect(await stale.confirmAdminBootstrapped()).toBe(true);
+		expect(await stale.isAdminBootstrapped()).toBe(true);
+		vi.spyOn(kvProvider, 'publish').mockRejectedValueOnce(new Error('kv down'));
+		await writer.releaseAdminBootstrap();
+		expect(await stale.isAdminBootstrapped()).toBe(true);
+		expect(await stale.confirmAdminBootstrapped()).toBe(false);
+		expect(await stale.isAdminBootstrapped()).toBe(false);
+	});
+
+	it('refuses to start when the setup token cannot be stored', async () => {
+		useSelfHostedProduction();
+		const pod = createPod();
+		vi.spyOn(pod, 'createSetupTokenIfAbsent').mockRejectedValueOnce(new Error('database down'));
+		await expect(ensureSetupToken(pod, accountExists)).rejects.toThrow('database down');
+	});
+});
+
 describe('InstanceConfigRepository concurrent writes', () => {
 	describe('in memory', () => {
 		describeConcurrentInstanceConfigWrites(async () => new InMemoryCassandraQueryExecutor());
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later

 import crypto from 'node:crypto';
+import {createUserID, type UserID} from '@app/api/BrandedTypes';
 import {Config} from '@app/api/Config';
 import type {APIConfig, BlueskyOAuthConfig, BlueskyOAuthKeyConfig} from '@app/api/config/APIConfig';
 import type {StoredLimitConfig} from '@app/api/constants/LimitConfig';
@@ -32,6 +33,7 @@ import {
 import {InstanceConfigCache} from '@app/api/instance/InstanceConfigCache';
 import {setCachedConfiguredLegalUrls} from '@app/api/instance/LegalUrls';
 import {getDefaultProductName, setCachedProductName} from '@app/api/instance/ProductName';
+import {isSetupTokenEnforced} from '@app/api/instance/SetupToken';
 import {normalizeSsoAllowedEmailDomains} from '@app/api/instance/SsoConfigValidation';
 import {Logger} from '@app/api/Logger';
 import {isStoredLimitConfig} from '@app/api/limits/LimitConfigValidation';
@@ -44,6 +46,7 @@ import {
 import {InstanceConfiguration, Users} from '@app/api/Tables';
 import {DEFAULT_DECAY_CONSTANTS, DEFAULT_RENEWAL_CONSTANTS} from '@app/api/utils/AttachmentDecay';
 import {isJsonRecord} from '@app/api/utils/JsonBoundaryUtils';
+import {randomBase64Url, secretMatchesHash, sha256Hex} from '@app/api/utils/SecretHash';
 import {
 	type AccountIdentityMode,
 	AccountIdentityModes,
@@ -120,6 +123,8 @@ const REGISTRATION_URLS_KEY = 'registration_urls';
 const REGISTRATION_PENDING_APPROVALS_KEY = 'registration_pending_approvals';
 const APP_PUBLIC_CONFIG_KEY = 'app_public_config';
 const ADMIN_BOOTSTRAP_KEY = 'admin_bootstrapped';
+const ADMIN_BOOTSTRAP_USER_ID_KEY = 'admin_bootstrap_user_id';
+const SETUP_TOKEN_HASH_KEY = 'setup_token_hash';
 const INSTANCE_POLICY_CONFIG_KEY = 'instance_policy_config';
 const LIMIT_CONFIG_KEY = 'limit_config';
 const INSTANCE_INTEGRATIONS_CONFIG_KEY = 'instance_integrations_config';
@@ -1484,8 +1489,95 @@ export class InstanceConfigRepository {
 		return (await this.getConfig(ADMIN_BOOTSTRAP_KEY)) === 'true';
 	}

-	async markAdminBootstrapped(): Promise<void> {
-		await this.setConfig(ADMIN_BOOTSTRAP_KEY, 'true');
+	async confirmAdminBootstrapped(): Promise<boolean> {
+		const cache = this.configCache;
+		const stored = (await this.fetchConfigFromDatabase(ADMIN_BOOTSTRAP_KEY)) === 'true';
+		if (stored !== (await this.isAdminBootstrapped())) cache.update(ADMIN_BOOTSTRAP_KEY, stored ? 'true' : 'false');
+		return stored;
+	}
+
+	async claimAdminBootstrap(userId: UserID | null = null): Promise<boolean> {
+		const cache = this.configCache;
+		const {written} = await this.compareAndSetStoredValue(cache, ADMIN_BOOTSTRAP_KEY, (raw) => ({
+			value: raw === 'true' ? null : 'true',
+			result: undefined,
+		}));
+		if (!written) return false;
+		await this.recordAdminBootstrapClaimant(cache, userId);
+		await this.publishAdminBootstrapRefresh(cache.sourceId);
+		return true;
+	}
+
+	private async recordAdminBootstrapClaimant(cache: InstanceConfigCache, userId: UserID | null): Promise<void> {
+		const claimant = userId?.toString() ?? '';
+		try {
+			await this.compareAndSetStoredValue(cache, ADMIN_BOOTSTRAP_USER_ID_KEY, (raw) => ({
+				value: (raw ?? '') === claimant ? null : claimant,
+				result: undefined,
+			}));
+		} catch (error) {
+			Logger.error({error}, 'Could not record which account claimed the admin bootstrap');
+		}
+	}
+
+	async getUnconfirmedAdminBootstrapClaimant(): Promise<UserID | null> {
+		const [bootstrapped, claimant] = await Promise.all([
+			this.fetchConfigFromDatabase(ADMIN_BOOTSTRAP_KEY),
+			this.fetchConfigFromDatabase(ADMIN_BOOTSTRAP_USER_ID_KEY),
+		]);
+		if (bootstrapped !== 'true' || !claimant || !/^\d+$/.test(claimant)) return null;
+		return createUserID(BigInt(claimant));
+	}
+
+	async releaseAdminBootstrap(): Promise<void> {
+		const cache = this.configCache;
+		const {written} = await this.compareAndSetStoredValue(cache, ADMIN_BOOTSTRAP_KEY, (raw) => ({
+			value: raw === 'true' ? 'false' : null,
+			result: undefined,
+		}));
+		if (written) await this.publishAdminBootstrapRefresh(cache.sourceId);
+	}
+
+	private async publishAdminBootstrapRefresh(sourceId: string): Promise<void> {
+		try {
+			await this.publishRefresh(sourceId);
+		} catch (error) {
+			Logger.error(
+				{error},
+				'Could not publish the admin bootstrap change. Other API processes see it after the next instance config change or a restart',
+			);
+		}
+	}
+
+	async isSetupTokenGateOpen(): Promise<boolean> {
+		return isSetupTokenEnforced(Config) && !(await this.isAdminBootstrapped());
+	}
+
+	async isSetupTokenRequired(): Promise<boolean> {
+		return (await this.isSetupTokenGateOpen()) && !(await this.getAppPublicConfig()).setup.configured;
+	}
+
+	async createSetupTokenIfAbsent(): Promise<string | null> {
+		const token = randomBase64Url(32);
+		const {written} = await this.compareAndSetStoredValue(this.configCache, SETUP_TOKEN_HASH_KEY, (raw) => ({
+			value: raw ? null : sha256Hex(token),
+			result: undefined,
+		}));
+		return written ? token : null;
+	}
+
+	async verifySetupToken(presented: string | null | undefined): Promise<boolean> {
+		const expectedHash = Config.instance.setup.token
+			? sha256Hex(Config.instance.setup.token)
+			: await this.fetchConfigFromDatabase(SETUP_TOKEN_HASH_KEY);
+		return secretMatchesHash(presented, expectedHash);
+	}
+
+	async burnSetupToken(): Promise<void> {
+		await this.compareAndSetStoredValue(this.configCache, SETUP_TOKEN_HASH_KEY, (raw) => ({
+			value: raw ? '' : null,
+			result: undefined,
+		}));
 	}

 	async getAccountIdentity(): Promise<AccountIdentity> {
@@ -9,11 +9,13 @@ import {
 	isDiscoveryNotModified,
 	nextDiscoveryValidators,
 } from '@app/api/instance/DiscoveryValidators';
+import {assertSetupToken} from '@app/api/instance/SetupToken';
 import {RateLimitMiddleware} from '@app/api/middleware/RateLimitMiddleware';
 import {OpenAPI} from '@app/api/middleware/ResponseTypeMiddleware';
 import {RateLimitConfigs} from '@app/api/RateLimitConfig';
 import {isBillingActive, isPremiumTieringActive, isStripeServiceable} from '@app/api/stripe/BillingConfigCache';
 import type {HonoEnv} from '@app/api/types/HonoEnv';
+import {requireConfiguredClientIp} from '@app/api/utils/RequestClientIp';
 import {Validator} from '@app/api/Validator';
 import {AccountIdentityModes, TagStyles} from '@fluxer/constants/src/AccountIdentityConstants';
 import {API_CODE_VERSION} from '@fluxer/constants/src/AppConstants';
@@ -130,10 +132,13 @@ export function InstanceController(app: Hono<HonoEnv>) {
 					instanceConfigRepository.getDomainMigrationConfig(),
 					instanceConfigRepository.getAccountIdentity(),
 				]);
-			const accountIdentityLocked =
+			const openSetup =
 				Config.instance.selfHosted && !appPublicConfig.setup.configured
-					? await instanceConfigRepository.isAccountIdentityLocked()
-					: undefined;
+					? {
+							account_identity_locked: await instanceConfigRepository.isAccountIdentityLocked(),
+							setup_token_required: await instanceConfigRepository.isSetupTokenRequired(),
+						}
+					: {};
 			const discovery = buildDiscoveryResponse(
 				buildDiscoveryStaticInput(
 					gifService,
@@ -142,7 +147,7 @@ export function InstanceController(app: Hono<HonoEnv>) {
 						setup: {
 							...appPublicConfig.setup,
 							admin_url: Config.endpoints.admin || null,
-							...(accountIdentityLocked === undefined ? {} : {account_identity_locked: accountIdentityLocked}),
+							...openSetup,
 						},
 					},
 					{
@@ -187,15 +192,23 @@ export function InstanceController(app: Hono<HonoEnv>) {
 			security: [],
 			tags: ['Instance'],
 			description:
-				'Sets how people sign in on a new self-hosted instance, and for email sign-in whether usernames are unique with no tag. Username sign-in always uses unique usernames. It works only before setup is finished and before the first account exists. After that it fails with ACCOUNT_IDENTITY_LOCKED.',
+				'Sets how people sign in on a new self-hosted instance, and for email sign-in whether usernames are unique with no tag. Username sign-in always uses unique usernames. It works only before setup is finished and before the first account exists. After that it fails with ACCOUNT_IDENTITY_LOCKED. While the instance requires a setup token, the request must send it as setup_token.',
 		}),
 		async (ctx) => {
-			const {mode, tag_style} = ctx.req.valid('json');
+			const {mode, tag_style, setup_token} = ctx.req.valid('json');
+			const instanceConfigRepository = ctx.get('instanceConfigRepository');
+			const {config, rateLimit, cache} = ctx.get('apiContext').services;
+			await assertSetupToken({
+				rateLimit,
+				config,
+				repository: instanceConfigRepository,
+				presented: setup_token,
+				clientIp: requireConfiguredClientIp(ctx.req.raw, config.proxy),
+			});
 			if (mode === AccountIdentityModes.USERNAME && tag_style === TagStyles.RANDOM) {
 				throw InputValidationError.fromCode('tag_style', ValidationErrorCodes.TAG_STYLE_REQUIRES_EMAIL_SIGN_IN);
 			}
-			const instanceConfigRepository = ctx.get('instanceConfigRepository');
-			const identity = await withAccountIdentitySetupLock(ctx.get('apiContext').services.cache, async () => {
+			const identity = await withAccountIdentitySetupLock(cache, async () => {
 				if (await instanceConfigRepository.isAccountIdentityLocked()) {
 					throw new AccountIdentityLockedError();
 				}
@@ -0,0 +1,110 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+import type {UserID} from '@app/api/BrandedTypes';
+import {Config} from '@app/api/Config';
+import type {APIConfig} from '@app/api/config/APIConfig';
+import type {InstanceConfigRepository} from '@app/api/instance/InstanceConfigRepository';
+import {Logger} from '@app/api/Logger';
+import {createRateLimitError} from '@app/api/utils/RateLimitUtils';
+import {ValidationErrorCodes} from '@fluxer/constants/src/ValidationErrorCodes';
+import {InputValidationError} from '@fluxer/errors/src/domains/core/InputValidationError';
+import {getSameIpDecisionKey} from '@fluxer/ip_utils/src/IpAddress';
+import type {IRateLimitService} from '@pkgs/rate_limit/src/IRateLimitService';
+import {ms} from 'itty-time';
+
+const SETUP_TOKEN_FAILURE_MAX_ATTEMPTS = 10;
+const SETUP_TOKEN_FAILURE_WINDOW_MS = ms('30 minutes');
+
+export function isSetupTokenEnforced(config: APIConfig): boolean {
+	return config.instance.selfHosted && (config.nodeEnv === 'production' || config.instance.setup.token !== null);
+}
+
+async function releaseAdminBootstrapOfMissingAccount(
+	repository: InstanceConfigRepository,
+	userExists: (userId: UserID) => Promise<boolean>,
+): Promise<void> {
+	const claimant = await repository.getUnconfirmedAdminBootstrapClaimant();
+	if (claimant === null || (await userExists(claimant))) return;
+	await repository.releaseAdminBootstrap();
+	Logger.warn(
+		{user_id: claimant.toString()},
+		'The account that claimed the admin bootstrap does not exist. The claim is released and the setup token applies again',
+	);
+}
+
+export async function ensureSetupToken(
+	repository: InstanceConfigRepository,
+	userExists: (userId: UserID) => Promise<boolean>,
+): Promise<void> {
+	if (!isSetupTokenEnforced(Config)) return;
+	await releaseAdminBootstrapOfMissingAccount(repository, userExists);
+	if (!(await repository.isSetupTokenGateOpen())) return;
+	if (Config.instance.setup.token !== null) {
+		Logger.info('Setup token read from FLUXER_SETUP_TOKEN');
+		return;
+	}
+	const token = await repository.createSetupTokenIfAbsent();
+	if (token === null) {
+		Logger.info(
+			'A setup token from an earlier start is still unused. Set FLUXER_SETUP_TOKEN to replace it if it is lost',
+		);
+		return;
+	}
+	Logger.warn(
+		{setup_token: token},
+		'Setup token generated. This instance has not recorded an admin account yet. The registration that presents this token becomes an admin. It is shown once',
+	);
+}
+
+export async function clearUsedSetupToken(repository: InstanceConfigRepository): Promise<void> {
+	try {
+		await repository.burnSetupToken();
+	} catch (error) {
+		Logger.error({error}, 'Could not clear the stored setup token after the admin bootstrap was claimed');
+	}
+}
+
+export async function assertSetupToken(params: {
+	rateLimit: IRateLimitService;
+	config: APIConfig;
+	repository: InstanceConfigRepository;
+	presented: string | null | undefined;
+	clientIp: string;
+}): Promise<boolean> {
+	const {rateLimit, config, repository, clientIp} = params;
+	if (!isSetupTokenEnforced(config)) return false;
+	const setupConfigured = (await repository.getAppPublicConfig()).setup.configured;
+	const adminBootstrapped = setupConfigured
+		? await repository.isAdminBootstrapped()
+		: await repository.confirmAdminBootstrapped();
+	if (adminBootstrapped) return false;
+	const token = params.presented?.trim();
+	if (!token) {
+		if (!setupConfigured) {
+			throw InputValidationError.fromCode('setup_token', ValidationErrorCodes.SETUP_TOKEN_REQUIRED);
+		}
+		return false;
+	}
+	const failureLimit = config.dev.relaxRegistrationRateLimits
+		? null
+		: {
+				identifier: `setup-token:ip:${getSameIpDecisionKey(clientIp) ?? clientIp}`,
+				maxAttempts: SETUP_TOKEN_FAILURE_MAX_ATTEMPTS,
+				windowMs: SETUP_TOKEN_FAILURE_WINDOW_MS,
+			};
+	if (failureLimit) {
+		const failureState = await rateLimit.peekLimit(failureLimit);
+		if (failureState.remaining === 0) {
+			throw createRateLimitError({
+				...failureState,
+				allowed: false,
+				retryAfter: Math.ceil(failureLimit.windowMs / failureLimit.maxAttempts / 1000),
+			});
+		}
+	}
+	if (!(await repository.verifySetupToken(token))) {
+		if (failureLimit) await rateLimit.checkLimit(failureLimit);
+		throw InputValidationError.fromCode('setup_token', ValidationErrorCodes.SETUP_TOKEN_INVALID);
+	}
+	return true;
+}
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later

+import {createHash} from 'node:crypto';
 import {createAuthHarness, createTestAccount, setUserACLs} from '@app/api/auth/tests/AuthTestUtils';
 import {getConfig} from '@app/api/Config';
 import {getCachedAccountIdentity, getCachedAccountIdentityMode} from '@app/api/instance/AccountIdentityModeCache';
@@ -14,10 +15,12 @@ import {ValidationErrorCodes} from '@fluxer/constants/src/ValidationErrorCodes';
 import {afterAll, afterEach, beforeAll, beforeEach, describe, expect, it, vi} from 'vitest';

 const ACCOUNT_IDENTITY_CONFIG_KEY = 'account_identity_config';
+const SETUP_TOKEN = 'setup-token-for-tests-0123456789-abcdefghijklmnopqrstuvwxyz';
+const WRONG_SETUP_TOKEN = 'wrong-setup-token-0123456789-abcdefghijklmnopqrstuvwxyz';

 interface DiscoveryResponse {
 	features: {account_identity: string; emails_enabled: boolean; tag_style: string};
-	app_public: {setup: {configured: boolean; account_identity_locked?: boolean}};
+	app_public: {setup: {configured: boolean; account_identity_locked?: boolean; setup_token_required?: boolean}};
 }

 interface AdminInstanceConfigResponse {
@@ -33,6 +36,7 @@ describe('Account identity mode', () => {
 	let originalSetupConfigured: boolean;
 	let originalAccountIdentity: typeof config.instance.accountIdentity;
 	let originalTagStyle: typeof config.instance.tagStyle;
+	let originalSetupToken: typeof config.instance.setup.token;

 	beforeAll(async () => {
 		harness = await createAuthHarness();
@@ -45,6 +49,7 @@ describe('Account identity mode', () => {
 		originalSetupConfigured = config.instance.setup.configured;
 		originalAccountIdentity = config.instance.accountIdentity;
 		originalTagStyle = config.instance.tagStyle;
+		originalSetupToken = config.instance.setup.token;
 	});
 	afterEach(() => {
 		vi.restoreAllMocks();
@@ -53,6 +58,7 @@ describe('Account identity mode', () => {
 		config.instance.setup.configured = originalSetupConfigured;
 		config.instance.accountIdentity = originalAccountIdentity;
 		config.instance.tagStyle = originalTagStyle;
+		config.instance.setup.token = originalSetupToken;
 		repository.clearCacheForTesting();
 	});
 	afterAll(async () => {
@@ -239,7 +245,7 @@ describe('Account identity mode', () => {

 	it('stamps email when the admin was bootstrapped', async () => {
 		useFreshSelfHostedInstance();
-		await repository.markAdminBootstrapped();
+		await repository.claimAdminBootstrap();
 		await repository.ensureAccountIdentityMode();
 		expect(await readStoredRow()).toMatchObject({mode: AccountIdentityModes.EMAIL, source: 'existing_instance'});
 	});
@@ -321,7 +327,7 @@ describe('Account identity mode', () => {
 	it('skips the users probe when a cheaper signal already decides', async () => {
 		useFreshSelfHostedInstance();
 		const probe = vi.spyOn(repository as unknown as {hasAnyUser: () => Promise<boolean>}, 'hasAnyUser');
-		await repository.markAdminBootstrapped();
+		await repository.claimAdminBootstrap();
 		await repository.ensureAccountIdentityMode();
 		expect(await readStoredRow()).toMatchObject({mode: AccountIdentityModes.EMAIL, source: 'existing_instance'});
 		expect(await repository.isAccountIdentityLocked()).toBe(true);
@@ -540,6 +546,77 @@ describe('Account identity mode', () => {
 		});
 	});

+	describe('setup token', () => {
+		async function putModeWithToken(setupToken?: string) {
+			return await createBuilderWithoutAuth<{
+				mode?: string;
+				tag_style?: string;
+				errors?: Array<{path: string; code: string}>;
+			}>(harness)
+				.put('/instance/setup/account-identity')
+				.body(
+					setupToken === undefined
+						? {mode: AccountIdentityModes.EMAIL}
+						: {mode: AccountIdentityModes.EMAIL, setup_token: setupToken},
+				)
+				.executeRaw();
+		}
+
+		it('reports in discovery whether registration needs the setup token', async () => {
+			useFreshSelfHostedInstance();
+			await repository.ensureAccountIdentityMode();
+			expect((await fetchDiscovery()).app_public.setup.setup_token_required).toBe(false);
+			config.instance.setup.token = SETUP_TOKEN;
+			const {text, json} = await createBuilderWithoutAuth<DiscoveryResponse>(harness)
+				.get('/.well-known/fluxer')
+				.executeRaw();
+			expect(json.app_public.setup.setup_token_required).toBe(true);
+			expect(text).not.toContain(SETUP_TOKEN);
+			expect(text).not.toContain(createHash('sha256').update(SETUP_TOKEN).digest('hex'));
+			await repository.claimAdminBootstrap();
+			expect((await fetchDiscovery()).app_public.setup.setup_token_required).toBe(false);
+			await repository.setAppPublicConfig({setup: {configured: true}});
+			expect((await fetchDiscovery()).app_public.setup).not.toHaveProperty('setup_token_required');
+		});
+
+		it('leaves the setup token out of discovery on the hosted service', async () => {
+			config.instance.selfHosted = false;
+			config.instance.setup.token = SETUP_TOKEN;
+			await repository.setAppPublicConfig({setup: {configured: false}});
+			expect((await fetchDiscovery()).app_public.setup).not.toHaveProperty('setup_token_required');
+		});
+
+		it('needs the setup token to choose the sign-in method while one is required', async () => {
+			useFreshSelfHostedInstance();
+			await repository.ensureAccountIdentityMode();
+			config.instance.setup.token = SETUP_TOKEN;
+			const missing = await putModeWithToken();
+			expect(missing.response.status).toBe(400);
+			expect(missing.json.errors?.map(({path, code}) => ({path, code}))).toEqual([
+				{path: 'setup_token', code: ValidationErrorCodes.SETUP_TOKEN_REQUIRED},
+			]);
+			const wrong = await putModeWithToken(WRONG_SETUP_TOKEN);
+			expect(wrong.response.status).toBe(400);
+			expect(wrong.json.errors?.map(({path, code}) => ({path, code}))).toEqual([
+				{path: 'setup_token', code: ValidationErrorCodes.SETUP_TOKEN_INVALID},
+			]);
+			expect(await readStoredRow()).toMatchObject({mode: AccountIdentityModes.USERNAME});
+			const correct = await putModeWithToken(SETUP_TOKEN);
+			expect(correct.response.status).toBe(200);
+			expect(correct.json).toEqual({mode: AccountIdentityModes.EMAIL, tag_style: 'none'});
+			expect(await readStoredRow()).toMatchObject({mode: AccountIdentityModes.EMAIL, source: 'setup'});
+		});
+
+		it('chooses the sign-in method without a setup token when none is required', async () => {
+			useFreshSelfHostedInstance();
+			await repository.ensureAccountIdentityMode();
+			const tokenless = await putModeWithToken();
+			expect(tokenless.response.status).toBe(200);
+			const ignored = await putModeWithToken(WRONG_SETUP_TOKEN);
+			expect(ignored.response.status).toBe(200);
+		});
+	});
+
 	describe('admin instance config', () => {
 		async function fetchAdminConfig(token: string): Promise<AdminInstanceConfigResponse> {
 			return await createBuilder<AdminInstanceConfigResponse>(harness, token).get('/admin/instance/config').execute();
@@ -47,6 +47,7 @@ import {InstanceConfigRepository} from '@app/api/instance/InstanceConfigReposito
 import {type LegalUrls, resolveLegalUrls} from '@app/api/instance/LegalUrls';
 import {NatsConfigPublisher} from '@app/api/instance/NatsConfigPublisher';
 import {getInstanceProductName} from '@app/api/instance/ProductName';
+import {ensureSetupToken} from '@app/api/instance/SetupToken';
 import {InviteRepository} from '@app/api/invite/InviteRepository';
 import {Logger} from '@app/api/Logger';
 import {LimitConfigService} from '@app/api/limits/LimitConfigService';
@@ -482,6 +483,11 @@ export async function initializeServiceSingletons(): Promise<void> {
 			assertServiceSingletonInitializationActive(owner);
 			await getInstanceConfigRepository().ensureAccountIdentityMode();
 			assertServiceSingletonInitializationActive(owner);
+			await ensureSetupToken(
+				getInstanceConfigRepository(),
+				async (userId) => (await getUserRepository().findUnique(userId)) !== null,
+			);
+			assertServiceSingletonInitializationActive(owner);
 			await limitConfigService.initialize();
 			assertServiceSingletonInitializationActive(owner);
 			limitConfigService.setAsGlobalInstance();
@@ -11390,7 +11390,7 @@
 						"content": {"application/json": {"schema": {"$ref": "#/components/schemas/Error"}}}
 					}
 				},
-				"description": "Sets how people sign in on a new self-hosted instance, and for email sign-in whether usernames are unique with no tag. Username sign-in always uses unique usernames. It works only before setup is finished and before the first account exists. After that it fails with ACCOUNT_IDENTITY_LOCKED.",
+				"description": "Sets how people sign in on a new self-hosted instance, and for email sign-in whether usernames are unique with no tag. Username sign-in always uses unique usernames. It works only before setup is finished and before the first account exists. After that it fails with ACCOUNT_IDENTITY_LOCKED. While the instance requires a setup token, the request must send it as setup_token.",
 				"requestBody": {
 					"required": true,
 					"content": {
@@ -29472,6 +29472,10 @@
 					"tag_style": {
 						"description": "How usernames are tagged. Defaults to none. Username sign-in accepts only none",
 						"$ref": "#/components/schemas/TagStyleSchema"
+					},
+					"setup_token": {
+						"description": "Setup token of a new self-hosted instance. Required until the first admin account exists",
+						"type": ["string", "null"]
 					}
 				},
 				"required": ["mode"]
@@ -32830,6 +32834,10 @@
 						],
 						"enum": ["dark", "dark_legacy", "coal", "light", "system"],
 						"type": "string"
+					},
+					"setup_token": {
+						"description": "Setup token of a new self-hosted instance. Required until the first admin account exists",
+						"type": ["string", "null"]
 					}
 				}
 			},
@@ -33569,6 +33577,10 @@
 					"account_identity_locked": {
 						"description": "Present only while a self-hosted instance is unconfigured. True when the sign-in method can no longer change",
 						"type": "boolean"
+					},
+					"setup_token_required": {
+						"description": "Present only while a self-hosted instance is unconfigured. True when registration needs the setup token",
+						"type": "boolean"
 					}
 				},
 				"required": ["configured", "admin_url"],
@@ -6,7 +6,7 @@ import {afterAll, beforeAll, describe, expect, test} from 'vitest';

 // Mirrors the live BRL/TRY configuration after the repricing: the BRL slots point at the new list
 // prices, TRY is not configured at all (production has no TRY prices), and every retired price id
-// lives only in the legacy map.
+// is only in the legacy map.
 const MOCK_PRICES = {
 	monthlyUsd: 'price_monthly_usd',
 	monthlyBrl: 'price_1TMbqsFPC94Os7FdfElrIIaZ',